NEWEST REVISION: Thursday February 3, 2005

General Comments:

1.  Check all of the Figure numbers, they have been rearranged and some may be added.

2.  All references to figures should be parenthetical

3.  Note that Drought has moved to section 1

4.  Comments were only made through the Water Use, Demand, and Demographics section.

To Be Continued

1.  Write up for the NDVI process

2.  An updated map of the lake level change area

3.  NDVI region map

4.  Close up image of interesting NDVI areas (depicting spatial variability, possibly 2)

5.  NDVI histogram?

Jenn Carter:

There are a few places where I think we need to talk about the results etc.. Specifically the paragraph on Pg 6-7, the PHDI thing (maybe find an equation – I couldn’t find one) and also I didn’t know what you meant by ‘endnote this paragraph” on pg 13

****I left the figures alone b-c I know jen constanza was going to work on that.. so anything that involved figures or captions I am waiting on b-c I don’t know what is going where***.. it should be relatively simple to fix after we get the new figures in the doc...

REVISION – 2/4/05

Jen Costanza:

I am still waiting for Fan to give me the map documents/data for Fig 1. I will update that figure with some sort of US map inset.

I am also trying to figure out which population graph should be used instead of the one we currently have.

I haven’t updated figure 9 yet either (lake change).

I tried to change the caption for Figure 6 (snowfall) as was suggested, but it appears that this is stated in the text, and the caption may either be redundant or possibly incorrect…

What is the other PHDI long-term graph?

I changed the references to figures in the text and made them parenthetical (I hope I got them all!).
Case Study of Lake Powell:

Impacts of Drought Conditions In the American Southwest

Lake Powell from above Wahweap Marina (Wikipedia, the free encyclopedia)

The University of North Carolina at Chapel Hill

Geog 177: Introduction to Remote Sensing of the Environment

Fall semester 2004

Dr. Aaron Moody, professor and project advisor

Monica Lipscomb, teaching assistant and project coordinator

Prepared By:

Brad Bennet, Lindsay Berk, Alec Bethune, Michael Cain, Jennifer Carter, Fan Chen, Lane Cidlowski, Jennifer Costanza, Arjun Dongre, Malena Gordon, Rachael Hyde, Karen Kaufman, Jordan Kern, Joshua Morris, Jesse Prentice-Dunn, Liza Schillo, Christina Schubert, Sarah Shelton, Preston Sloop, Elizabeth Sutherland, Kate Vlach, Eric Witz, and Ling Zhang

INTRODUCTION

In his well-known Farmer’s Almanac, Benjamin Franklin notes that “When the well is dry, we learn the worth of water” (Franklin, 1773). Water is commonly thought of as a resource with an endless supply; however, less than 1% of the world’s water supply is available as fresh water for human use and consumption (Mackenzie, 2003). The quantity of our precious resource is further affected by global climate change. One possible consequence of global climate change is an acceleration of the global hydrological cycle. It is likely that this cycle will lead to an increase in extreme events, such as floods and droughts (Dai, Tenberth, & Karl, 1998; Ziegler, et. al., 2003). Some studies are already indicating that there was a significant increase in the global frequency of floods during the twentieth century; these studies also predict will occur more often in the future (Milly, Wetherald, Dunne, & Delworth, 2002). Increasing global temperatures, especially in arid regions like the Southwest United States, have increased evaporation rates while suppressing precipitation rates. This has led to drought conditions in places like Russia, central Africa and the Southwest U.S. (Ziegler, et. al., 2003).

Generally, the western half of the United States receives less than 20 inches of rainfall per year while the eastern half greater than 20 inches (Reisner, 1993). The Southwestern U.S has seen unusually low quantities of precipitation over the past five years, even compared to the normally arid conditions in this region.

While annual precipitation has decreased across the region, water demand has increased. The American Water Works Association estimates U.S. homes, farms, and industries collectively use approximately 346,800 million gallons per day of freshwater (2004). In the agricultural sector alone, there is a need for 1,000 tons of water to raise 1 ton of grain and 16,000 tons of water to raise 1 ton of beef (Bruce, 2003). The increasing water needs of the private, agricultural, and industrial sectors in the Southwestern U.S. have amplified the pressure for reservoirs to deliver, especially during this recent period of drought. The drought has decreased reservoir levels throughout the Southwest due to increased evaporation, decreased inflow, and increased demand.

Located along the Arizona-Utah border, Lake Powell is the second largest reservoir in the country. In order to harness the power of the Colorado River, the Glen Canyon Dam was constructed. After completion in 1964, the backup caused by the dam formed Lake Powell, a major source of water in the region (Farmer, 1999). Due to a significant increase in population, water demands in the U.S. Southwest have increased, particularly in the Colorado River Basin. Consequently, the reservoir has experienced a dramatic reduction in water levels. During the summer of 2004, the lake fell 21 inches per week. Lake levels have not rebounded, as the lake is currently less than half full, down 130 feet from its pre-drought depth (Watson, 2004). Decreasing lake levels has both created concern about future water supply and hurt local economies due to lack of tourism which generated a large majority of its commerce. It is predicted that faced with a lingering drought a growing population will demand even larger amounts of water. With the onset of shrinking water supplies and drying wells, dramatic consequences could be forthcoming, unless the worth of water is realized. Through data analysis, this paper aims to explain why and how Lake Powell is shrinking.

8

Figure 1. Map of the study area showing climate and hydrologic stations used in our analysis. The image is shown as a 432 near infrared composite, with the near infrared band drawn in red, red drawn in green, and green drawn in blue. The image was taken by ETM+ sensors on Landsat-7 in 1999 and 2000 (Data source: United States Geological Survey, 2004).

8

DROUGHT

There are four different categories of drought: meteorological, hydrological, agricultural, and socio-economic. Meteorological drought occurs when the level of precipitation falls below average for a specific area. Hydrological drought transpires when the water levels of bodies of water (i.e. lakes, rivers, reservoirs, and ground water) are below normal. There is often a lag between hydrological and meteorological drought due to the fact that water levels are affected by a larger number of variables and are also slower to respond to a reduction in precipitation. If the water needs of vegetation aren’t met, the area in subject will experience an agricultural drought. The last category, socio-economic drought, is an indicator of how much supply exceeds demand of crop due to water shortages.

Although numerous drought indices are available, the Palmer Hydrological Drought Index (PHDI) was chosen for the drought analysis in the Lake Powell region. The PHDI accounts for long-term hydrological factors, such as groundwater and reservoir levels, thus allowing for effective monitoring of the effects of drought on a reservoir such as Lake Powell. The PHDI relies more onBecause the PHDI relies more on hydrological data than precipitation data.. This is why , the PHDI reacts to changing conditions more slowly than the Palmer Drought Severity Index (PDSI). PHDI values are standardized on a scale of –6 to 6, where negative values are indicative of drought and positive values are indicative of periods of moisture (Table 1). The PHDI data used in this analysis were obtained from the NCDC (1994). Observers at cooperative stations, in different climatic divisions, collected values used in these calculations. The data are based on temperature and precipitation. The NCDC data are a monthly average corrected for “time bias,” which is introduced by the time of day the data are collected. The data are calibrated using the period 1895-1990 (Karl, 1986).

Table 1 - Classes for Wet and Dry Periods (NCDC, 1994)

Analysis of Data

The drought analysis is based on averaged monthly PHDI, from the years 1990 – 2004, for two climate divisions encompassing the Lake Powell region: Utah climate division #7 and Arizona climate division #2 (Fig. 2). It can be seen that there are three periods of extreme drought; they occurred in 1996, 2000, and 2002. The most significant periods of moisture occurred in 1993 and 1995. Beginning in 1993, with an almost continuous drought condition since 2001, the trend is towards increasing severities severity of drought. Drought-like conditions are highly seasonal, particularly in May-Aug when it is the worst . (Fig. 2).

Figure 2. Short term plot (1990-2004) of monthly average drought index (average PHDI)for the Utah and Arizona climate divisions. Note the 12-month moving average trend line.

Because in 2000, PHDI was at or below normal levels, further analysis was performed on the differences between the Arizona and Utah climate divisions[1]. For both climate divisions, the years 1996, 2000, and 2002 were shown to be times of extreme drought while 1993 and 1995 were shown as years of increased moisture. Arizona division #2 exhibits more extreme periods of drought than Utah division #7, as well as generally more extreme periods of moisture. However, the Utah climate region is probably the most important for this analysis, as it comprises a greater portion of the river basins that impact Lake Powell. The trend for both divisions, since 1993, is also one of increasing drought. It is difficult to determine from this analysis whether drought conditions will continue or if they are part of a multi-decade cycle. The drought seems to have reached a peak in 2002, which, according to the NCDC, was the driest on record for Utah. The 2002 peak drought year prompted Governor Napolitano of Arizona to issue an executive order in 2003, establishing a drought task force (Napolitano, 2003).

Long-term Trends

PHDI for the Lake Powell area shows a period of extreme drought around the turn of the twentieth century. At about this time, the Bureau of Reclamation, the government bureaucracy that would ultimately construct the dam that created Lake Powell, was established. A long period of increased moisture followed in the decade of 1910-1920. This period of moisture is significant in that it resulted in the overestimation of water reserves in Colorado, and when the Colorado River Compact was signed in 1922, a malapportionment of water supplies ensued (Reisner, 1993). A long period of relative drought followed until a decade of increased moisture occurred in the 1980’s (see Fig. 8, below).

In recent years, this drought continues to increase dramatically and has reached one of the worst in Arizona’s history and also one of the three longest cumulative droughts on record for the century. In light of the long-term data it appears that the recent period of drought may be cyclical in nature (Fig. 3). However, the shifting extremes exhibited in these results may be indicative of long-term climate change. According to the NCDC, the average temperature in Arizona has risen 3.6°F in the last century. Temperature is a component of the PHDI, and increased temperature leads to increased evapo-transpiration and drought. This change has taken place despite increased precipitation.

Figure 3. Long term plot of drought index (PHDI) anomalies in the Lake Powell Area for the period 1950-2004.

PRECIPITATION

A decrease in precipitation within the basins draining into Lake Powell is an element that has contributed to the shrinking of Lake Powell. To investigate this, total precipitation data were obtained from the Western Regional Climate Center (WRCC) and the National Climatic Data Center (NCDC, 1994) and collected for climate stations in Escalante, UT; Mexican Hat; UT, Hanksville, UT; and Monticello, UT. The yearly precipitation totals obtained from the WRCC are not completely accurate, as some of the daily entries were missing in the collection periods. However, this error was not significant enough to alter the obvious overall decreasing trend in annual rainfall since 1995.

Based on the data from four stations, average annual precipitation graphs were created. It can be seen that the long-term data (1950-2003) do not display a clear trend although the years since 2000 have been below average (Fig. 4).

Figure 4. Long term plot (1950-2003) of streamflow and precipitation anomalies in the immediate Lake Powell basin.

On the other hand, the short-term data (1995-2003) display a clear negative trend (Fig. 5). Therefore, it is concluded that a decrease in precipitation, although not a major causal agent, may be a factor in contributing to the current shrinking of Lake Powell.

Figure 5. Short term precipitation and streamflow averaged from stations immediately surrounding the Lake Powell basin.

In addition to rainfall, snowfall at higher elevations contributes to source water for Lake Powell. The snowfall data for this analysis were obtained from the SNOTEL (Snowpack Telemetry) data collection network (United States Department of Agriculture, National Resources Conservation Services [USDA, NRCS]). SNOTEL is operated by the NRCS in order to meet the agency’s congressional mandate to “measure snowpack in the mountains of the West and to forecast water supply” (USDA, NRCS). SNOTEL sites are located in remote high-mountain watersheds where access is difficult and restricted. While there are more than 600 SNOTEL sites in 11 Western states, this analysis was limited to those sites located in Utah and the Upper Colorado River/Lake Powell watershed. There was a consistent average annual snowfall from the greater Colorado River basin since 1990 and a decline in total annual precipitation (Fig. 6). These results indicate that while there has been a decrease in precipitation over the past decade, there has not been a change in snowfall at higher elevations.